8.3.0: The “Ready for the good times” release

8.3.0 (2019-02-22)

• Refactor parsing logic to mostly reside in the class files whose data structure is to be parsed (this should eventually allow us to unit-test specific parts of the parsing logic individually).
• Fix error in parsing calc expessions when the first operand is a negative number, thanks to @raxbg.
• Support parsing CSS4 colors in hex notation with alpha values, thanks to @raxbg.
• Swallow more errors in lenient mode, thanks to @raxbg.
• Allow specifying arbitrary strings to output before and after declaration blocks, thanks to @westonruter.
• No backwards-incompatible changes
• No deprecations